Grouting fissures in underground rock salt deposits

ABSTRACT

There is disclosed an improved method for grouting (sealing) a ground water conducting fault zone, fissure, or the like, such as has been inadvertently intersected when mining an underground salt deposit.

United States Patent 1 3,702,059 Jacoby 1 Nov. 7, 1972 [54] GROUTINGFISSURES IN [56] References Cited UNDERGROUND ROCK SALT DEPOSITS IUNITED STATES PATENTS 72 I t 1 Ch I H. b D It P 3,055,423 9/1962 Parker..61/35 X 1 es Jam a a 3,468,129 9/1969 Knutson ..61/36 R x [73]Assignee: International Salt Company, Clarks Summit, PrimaryExaminer-David J. Williamowsky 22] Filed: O 13 1971 AssistantExaminerPhilip C. Kannan Attorney-John B. Bean et al. 21 App]. No.:188,906 0 v [57] ABSTRACT U-S- Cl. There i di lo ed an improved methodfor grouting 299/5 (sealing) a ground water conducting fault zone, fis-[51] Int. Cl. ..E02d 19/16 Sure or the like, such as has beeninadvertently inter [58] Field of Search "61/35, 166/285 sected whenmining an underground salt deposit.

' 6 Claims, 3 Drawing Figures PATENTEDunv 1 I972 3.702.059

I N VENTOR. CHARLES H. JHCOBY ATTORNEYS GROUTING FISSURES IN UNDERGROUNDROCK SALT DEPOSITS BACKGROUND AND GENERAL DESCRIPTION OF THE INVENTIONThe invention relates to a method for grouting a water leaking fissurein an underground mass of sodium chloride rock salt or the like; and hasparticular appli cation to the problem of closing off such fissures fromwithin an underground mine opening.

' On occasion earth movements and/or other geological pressure forcessubject underground salt deposits to fracturing stresses, with theresult that mine openings thereinto will on such occasions intersectfracture zones or fissures which thereupon conduct ambient ground watersinto the mine workings. Conventional grouting methods are only partiallyeffective in such cases because the fissures are often too narrow topermit introduction of conventional sealing compounds,

reagents, or the like. The present invention takes advantage of the factthat air can be forced under pressure to penetrate into the tiniest ofcracks or crevices, and will flow through the narrowest of interstices;and also that when air is introduced into any body of liquid itnaturally rises therewithin and generates an air-lift effect against theliquid. The invention utilizes the fact that when ground water movesthrough an opening in a salt mass .the water dissolves salt in theprocess until it becomes a 100 percent saturated brine solution at theambient pressure/temperature conditions; and that such solutions may betriggered to convert into' solid recrystallized salt simply by bubblingair through the brine'solution.

By way of example, the invention is illustrated by the accompanyingdrawings wherein:

THE DRAWINGS FIG. 1 is a diagrammatic geological sectional view showinga typical salt mining operation in a salt dome: and illustrating how themine workings have inadvertently intersected a fault or fracture planein the salt deposit such as operates as a conduit permitting groundwaters to enter the mine workings;

FIG. 2 is an enlarged scale view of that portion of the mine, showing afirst step in preparation for sealing off the intersected fissure frominside the mine; and

FIG. 3 is a view of the sealing or grouting operation, taken assuggested by line 3--3 of FIG. 2.

As illustrated at FIG. 1, a salt dome (designated such as occurunderground in Louisiana, Texas and Alabama is typically mined bydrilling a vertical shaft 12 from the earth's surface downwardly intothe deposit'to the desired level, as determined by preliminary drillingsurveys. A room-and-pillar mining system (or some alternative system)such as indicated at 14 is then developed to reach out horizontally fromthe foot of the shaft 12. The salt product is then brought to thesurface to be processed, as in a surface plant illustrated at 16.

Due to earth movement forces thereon subsequent to their formation suchsalt domes typically develop spire fractures and/or fault planes asindicated at (FIGS. 1 and 2 of the drawing herewith). Whereas the saltdome per se comprises an extremely solid and water-tight mass, suchfissures therein provide conduits for seepage of ground waterstherethrough. Therefore,

whenever a mine working such as indicated at 14 is driven so as tointersect a fissure of this type the mine will become flooded unlessadequate pumping facilities are established and maintained.Alternatively, in some instances where the fissure is ofsufi'icientwidth, some conventional form of grouting may be employedwith some degree of success, perhaps sufficient to reduce the pumpingrequirements to an economically feasible level. The conventionalgrouting methods referred to usually involve the introduction (into thefissure, either from above or below) of some form of quick settingcement, or materials compounded to react and form solids that expand.However, such prior grouting methods are usually only partiallyeffective and are uncertain and unreliable as to permanence, and areinvariably quite expensive.

.1 When working at substantial depths underground the accompanyingground water pressure heads are enor- I like. At substantial depthsunderground even a fissure of no measurably appreciable width forexample will nevertheless leak water into the mine working, and it is toflow into a dimensionally minute but highly pressurized fissure, becausea gas will flow where a liquid cannot flow due to surfacetension/friction factors. Furthermore, the invention takes advantage ofthe fact that whenever a gas is forced under pressure into a body ofliquid of higher specific gravity, the gasautomatically bubbles upwardlythroughout the vertical extent of the body of liquid.

However, the major phenomenon upon which the present invention operatesderives from the fact that whenever ground waters percolate through areadily soluble mineral, such as sodium chloride salt, a brine solutionis thereby formed. When the rate of flow of solvent through the salt issufficiently slow that no constantly enlarging channel is washed throughthe mineral, the brine solution is the fissure will inevitably be anapproximately percent saturated salt solution. This means that at theexisting temperature the solution will accommodate no additionalproportion of salt without undergoing recrystallization.

In accordance with the present invention, assuming that the encounteredfissure is not of the type such as may be blocked off and grouted byconventional methods, the exit of the fissure seam will first becarefully surveyed with a view to determining the parameters of itsplane. A rock drill 22 or the like will then be set up in place as shownat FIG. 2 so as to direct a drill hole 24 through a substantial body ofsolid salt until the hole intersects the plane of the fissure 20 at asubstantial distance away from the elevation above the exit of thefissure into the mine working. Intersection of the fissure by the borehole as indicated at 25 will of course be recognized by the fact thatground waters will now come in through the bore hole.

Any suitable means for supplying air under pressure to the bore hole 24will now be applied such as by means of a portable air compressor unitas illustrated at 26 (FIG. 3); and the pressure thereof regulated sothat air will b e-injectedthrough the bore hole into the fis sure atasubstantial volumetric rate. The air should be dry, and preferably atan elevated temperature such as produced by an air compressor ascommonly used in mine workings. The dry warm air entering the fissureabsorbs moisture from the saturated salt solution in the fissure whichthereupon becomes supersaturated. The process of salt recrystallizationthereupon initiates, forming a curtain of descending seed crystals 28which grow until they solidly fill that portion of the fissure whichumbrellas the mine working. As the crystal growths proceed the suppliedair finds its way around,

through and between the growing crystals; all the while absorbing. waterfrom the solution until the fissure is sealed against descending liquidflow from above as explained hereinabove. e

It is noteworthy that when the air is first pumped into the fissure ittends to bubble upwardly throughout the brine solution within thefissure. Thus, the air-lift principle operates to carry the drying airupwardly while at the same time fanning-out horizontally within thefissure. Thus the seed crystals of salt form throughout the fissure,providing therein a curtain-like matrix of constantly growing crystals;thereby operatingeventually to seal off the fissure at a substantialelevation above and around the mine working.v The air-lif effectoperates to assist in balancing and/or overcoming the hydrostaticpressures accompanying the ambient ground waters, thereby stalling theirflow progress into the workings and providing an improvement of quietudefor salt recrystallization and plugging of the fissure as explainedhereinabove.

Whereas the specification hereinabove refers primarily to the use ofheated air as being the preferred form of gas to be employed for dryingthe in-flowing brine solution and precipitating salt to plug thefissure, it is to be understood that any other suitable water absorbinggas may be employed. It is also to be understood that the invention isparticularly efficacious because of the fact that when the solid saltparticles precipitate out of the brine solution in the fissure, theyweld themselves into integrally structured relation with the rock saltwalls of the fissure; whereby a unified crystalline and water imperviousstructure is provided having superior water sealing properties.

This sealing system is therefore far superior to conventional groutingmethods involving the use of foreign filler substances which do notbond/merge with the salt walls of the fissure, and in some cases tend toshrink after setting. Also, in some cases conventional groutingsubstances are exothermic while setting and thereby subject thefissurelwalls to deleterious expansion/contraction forces.

I claim; I

1. The method of reducing or preventing flow of a brine solution througha fissure in an underground rock saltdeposit into amine workingintersecting said fissure, said method comprising;

in ect ng drying gas mto said fissure at a volumetric rate sufficient topercolate through saidsolution while absorbing water from said solutionand thereby initiating recrystallization of solid salt from saidsolution, and continuing such ejection until solid salt crystallizesout. of said solution and salt crystals grow inside said fissure andattach to the walls thereof and to each other to provide a solidstructurally integrated plug of rock salt filling said fissure ambientto said mine working.

2. The method according to claim 1 wherein said drying gas is air. I

3. The method according to claim 2 wherein said air is heated. I

4. The method according to claim 1 wherein injection of said drying gasinto said fissure is accomplished by first drilling a bore hole througha solid rock salt boundary portion of the mine working so as tointersect said fissure at a location a substantial distance away fromthe mine working, and then coupling a source of pressured drying gasinto said bore hole for transmission therethrough and into said fissurefor dispersion in all directions within said fissure.

5. The method according to claim 4 wherein said drying gas is air.

6. The method according to claim 4 wherein said drying gas is heatedair.

1. The method of reducing or preventing flow of a brine solution througha fissure in an underground rock salt deposit into a mine workingintersecting said fissure, said method comprising; injecting drying gasinto said fissure at a volumetric rate sufficient to percolate throughsaid solution while absorbing water from said solution and therebyinitiating recrystallization of solid salt from said solution, andcontinuing such ejection until solid salt crystallizes out of saidsolution and salt crystals grow inside said fissure and attach to thewalls thereof and to each other to provide a solid structurallyintegrated plug of rock salt filling said fissure ambient to said mineworking.
 2. The method according to claim 1 wherein said drying gas isair.
 3. The method according to claim 2 wherein said air is heated. 4.The method according to claim 1 wherein injection of said drying gasinto said fissure is accomplished by first drilling a bore hole througha solid rock salt boundary portion of the mine working so as tointersect said fissure at a location a substantial distance away fromthe mine working, and then coupling a source of pressured drying gasinto said bore hole for transmission therethrough and into said fissurefor dispersion in all directions within said fissure.
 5. The methodaccording to claim 4 wherein said drying gas is air.
 6. The methodaccording to claim 4 wherein said drying gas is heated air.